Continue lab volunteering?

<p>I'm a senior. The only research experience I have is volunteering in a lab for 6 months and summer undergrad research program in the same lab for 4 months (So a total of 10 months). Since the end of the undergrad research program, I didn't work in a lab. Now I'm considering whether to go back to the lab to resume volunteering, but I'll only be able to devote about 6 hours a week. I heard that a minimum of 15 is ideal to be able to make a significant contribution. Should I still resume volunteering even if it's as little as 6 hours a week? If I volunteer only 6 hours per week, then the lab will most likely give me only or mostly grunt work, right?</p>